1. Field of the Invention
The present invention relates to a method for adjusting the maximum radiation direction of a radiation wave by use of diffraction gratings formed on the surface of a dielectric waveguide, and more particularly to a method for adjusting the radiation direction of radiation waves in an antenna, which uses a plurality of uniformly spaced diffraction gratings formed in the waveguide of the antenna while applying voltage to the diffraction gratings to vary the length of crystal lattices in the diffraction gratings, thereby achieving an improvement in the directivity of the radiation waves and an adjustment in the radiation direction of radiation waves.
2. Description of the Prior Art
Generally, antennas are conductors installed in the air to radiate or absorb electric waves. Such antennas are classified into those for the purpose of transmission and those for the purpose of reception in terms of their use purposes. In terms of the wavelength of an electric wave used, such antennas are also classified into those for medium frequency wave, those for short wave, and those for very high frequency wave. These antennas of different types have different operating principles and configurations, respectively. Such antennas are also classified into directional antennas and non-directional antennas in accordance with the radiation characteristic of an electric wave used. Also, such antennas have a variety of shapes, for example, I, T, and inverted-L shapes, etc.
FIG. 1 is a sectional view illustrating an antenna system which uses a dielectric waveguide having a conventional travelling-wave antenna configuration. The antenna system includes a tuning stub 1 arranged at the intermediate portion of the waveguide. The tuning stub 1 serves as a short circuit plate for matching a coaxial feed line 2 with a load. The coaxial feed line 2 consists of a coaxial cable and extends through the waveguide. The coaxial feed line 2 connects the antenna to a transmitter or receiver to feed electric power therebetween. The waveguide, which is denoted by the reference numeral 3, is a circular metal tubing waveguide having a hollow circular metal tube construction and serving as a high-pass filter. That is, the circular metal tubing waveguide 3 has a certain cut-off wavelength in a guide mode so that it prevents waves having a wavelength longer than the cut-off wavelength from passing therethrough. The waveguide 3 carries out a propagation at a guide wavelength different from an excitation wavelength therein. A polystyrene material, which is a typical material for antennas, fills the interior of the circular metal tubing waveguide 3. The polystyrene member 4 protrudes outwardly from the circular metal tubing wave guide 3.
In this antenna configuration, transmission/reception microwaves are axially input/output through the circuit metal tubing waveguide 3. The tuning stub 1 matches the circular metal tubing waveguide 3 with the coaxial feed line 2 serving as an electric power passage between the transmitter/receiver and the antenna. The circular metal tubing waveguide 3, the coaxial feed line 2, the end portion of the waveguide and the protruded portion of the polystyrene member 4 are set by different wavelengths, respectively, to obtain a travel of waves of appropriate wavelengths for a transmission of microwaves.
In such a conventional antenna, however, the travel direction of radiation waves coincides with the extension direction of the antenna. Furthermore, this antenna exhibits a degradation in directivity because the width of waves passing through the antenna is widened. Also, the dielectric system should use a phase modulator for adjusting the direction of radiation waves. As a result, the entire system is bulky. It is also impossible for the system to be used for millimeter waves having a high frequency and in the optical wave frequency band.
U.S. Pat. No. 5,237,334 (William M. Waters) discloses a focal plane antenna array for millimeter waves. The millimeter-wave focal plane antenna array comprises a means defining a planar array of a plurality of open ended waveguides which, in use, are disposed at the focal plane, and a microstrip detector means coupled to the waveguides for detecting the millimeter wave radiation received thereby. The microstrip detector means comprises a dielectric substrate affixed to the array defining means, and a plurality of separate, unconnected microstrip conductors embedded in the substrate. Each microstrip conductor is coupled to a respective one of the waveguides to receive the millimeter radiation therefrom. The microstrip detector means also comprises a diode detector being connected to each microstrip conductor for producing an output in accordance with the millimeter wave radiation coupled from a corresponding waveguide to the associated microstrip conductor. The millimeter-wave focal plane antenna array uses a plate made of a conductive material to adjust the direction of radiation waves. However, since the plate has a perforated structure, it is difficult for the plate to have a reduced thickness for its low-frequency use.